- This is a competitive renewal of a program that has investigated cytokines produced by keratinocytes and the influence that the cytokines have on recruiting leukocytes to the skin during immune and inflammatory processes. In the current proposal, the investigator focuses on an important cell that is normally found in tissues, including the skin, the dendritic cell. Skin, oral, and genital mucosal dendritic cells, which include both Langerhans cells and dermal dendritic cells, appear to belong to a distinct bone marrow/-derived lineage and are highly effective at presenting antigen in an immunogenic fashion to T cells. This capacity of dendritic cells and the capacity to grow large numbers of such cells in vitro have now allowed new dendritic cell-based approaches to immunotherapy. Mucosal dendritic cells are thought to be the first cells infected by HIV during heterosexual transmission; this occurs through their co-expression of CD4 and the chemokine receptor CCR5 and to a lesser extinct, CXCR4. Either in situ or after trafficking to lymph nodes, HIV-infected DCs can efficiently transfer HIV to CD4-positive T cells. Given the central importance of these cells to HIV disease and their potential role in experimental therapy of cancer and infectious diseases, there is very little understood about the ability of DCs or their precursors to exit peripheral blood and enter skin or mucosal tissues. This group of investigators have made the follow observations relevant to this process: (1) Human peripheral blood dendritic cells and epidermal SLCs express selectin ligand-related sLeX epitopes (HECA-452), multiple CC and CXC chemokines receptors, LFA-1 and VLA4. The selectin ligands are functional, as they can tether and roll under physiologic flow conditions on E and P selectin; (2) transgenic mice deficient in E and P selectin, as well as mice deficient in FT VII have diminished numbers of cutaneous dendritic cells; (3) transgenic mice expressing the chemokine MCP-1 under the control of an epidermal promoter exhibit large numbers of dendritic cells in dermis, at the dermal-epidermal junction and around hair follicles. The investigators hypothesize that under physiologic conditions, there is a dynamic trafficking of dendritic cells from blood into skin. These dendritic cells in peripheral blood exit into skin via a multi-step selectin/chemokine/CAM pathway. In the absence of tissue inflammation, they respond to low constitutive levels of cutaneous chemokines, endothelial selectins, and CAMs. When inflammation is present, dendritic cells employ the high levels of selectins and CAMs, as well as newly expressed chemokines, to extravasate even more efficiently. Once they have exited vessels, the investigators hypothesize that cytokines (including chemokines) produced by epidermis influence DC migration, differentiation, activation state, and function. Using defined in vitro assay systems to measure different parameters of each stop involved in the extravasation process, as well as in vivo transgenic murine models that overexpress or are deficient in the expression of selectins, their ligands, and chemokines, they will test these hypotheses in a rigorous and novel fashion.